Treatment of mouse bone marrow‐derived macrophages with the proinflammatory cytokine TNFα in the presence of M‐CSF and RANKL stimulates osteoclast differentiation in vitro.(15, 16, 17) We therefore investigated the requirement of this proinflammatory cytokine for macrophage recruitment and osteoclast differentiation in vivo in the medaka osteoporosis model. The gene discussed is TNFSF11; the disease is osteoporosis.